Gross examination of female 129/J mice revealed swelling and protrusion of the ventral vulva, with some mice exhibiting a hemorrhagic discharge. Forty seven of 106 mice ranging from 6 weeks to 9 months of age had vulvar lesions. Necropsy examination disclosed vulvar masses which appeared to develop spontaneously with age. Histological examination identified the vulvar masses as squamous cell carcinomas (SCC). Vulvar squamous cell carcinomas have not been reported in 129/J mice. However, sporadic cases of SCC have been reported in cattle, sheep, and primates and are associated with papilloma virus infection of the female lower genital tract in cattle and humans. The objectives of this study are to confirm this neoplasm as a SCC and to study its origin in 129/J and athymic nu/nu mice. Different size tumors from 129/J mice of different ages will be examined using light microscopy and EM methods to confirm the origin of the SCC. Also, tumors will be inoculated into nu/nu mice to determine the origin or growth of the tumors in nude mice.